A Common ResourceThe supply curve S, which shows the marginal private cost of production of the fishing industry, is composed of the individual supply curves of the individual fishers. But each fisher’s marginal private cost does not include the cost that his or her actions impose on others: the depletion of the common resource. As a result, the marginal social cost curve, MSC, lies above the supply curve; in an unregulated market, the quantity of the common resource used, QMKT, exceeds the efficient quantity of use, QOPT.